Well- I have a pair of six foot AllGlass tanks I got used about 7 years ago. These are very old tanks, They came with the AllGlass raised logo pasted to the class and it cannot be removed. I would bet these tanks are decades old. the glass on the 150 is 1/2 inch thich and 3/8 on the 125.
I have had 3 leakers. My first tank, a 45, developed a small leaks near the top after about 10-12 years, I had a used 75 in-wall tank that deveolped a leak in the bottom right corner. That tank was with me about 8 or 9 years and with the original owner for about 5. Finally, I di buy a 20L from Glasscages.com that leaked as soon as I filled it. Now those three leakers were out of about 35 tanks maybe a few more i have owned over the years. As time went by I sold some and then bought either bigger ones or down the road actually rebought the same size.
I do not reseal leakers, even the slow leakers. They get thrown out and replaced.
Here is the thing to consider about cars by way of an analogy. Whether you are talking an inexpensive Subaru or a top of the line Mercedes, you can end up with a lemon from either one. The same applies to tanks. From the minute they are made they are never treated in an Identical way. From how they are transported from factory to a store, how they are handled in the store and then we buy them. How you may man-hadle it into your car/truck, how you muscle it into place etc. all matter.
Then there are the everyday issues. When you set it up did you accidentally bang the glass, did you drop something onto the boittom doing the layout? How about using that bladed algae scraper, did you scrape silicon away by accident?
As for tempered glass, it is stronger and safer, But it will cost about 25% more. But the bigger problem is it has to be manufactured to the exact size needed as once it is tempered, it cannot be cut.
I am not sure about now, but in years past AllGlass offered tempered bottoms on certain sizes.
One last observation. If a tank breaks, that is the glass itself cracks or outright shatters, that is one thing. However, if it leaks at the joints, that is a silicone issue. The more expensive tank brands use ther same silicone as the Aqueon or Marineland tanks. Tanks must be sealed with 100% pure silicone. Brand does not matter in this respect. So the likely-hood of a silicone failure is equal in the more expensive and the most commonly used brands.
I do know this about tempered glass. In NY when we replacde two windows with a single very large pane of glass we had to have it made tempered because of the size. This was a regulation in NY, we had no choice. Theglass people explained to us the part about how it is made and that it cannot be cut down once it is tempered.